1. Field of the Invention
The present invention relates to an inner drum type image recording device in which a recording medium is set in close contact with and supported by an inner peripheral surface of a support which is formed in a circular-arc shape, and an image is recorded on the recording medium by rotating a spinner mirror and moving the spinner mirror in the axial direction of the support.
2. Description of the Related Art
In a CTP (computer-to-plate) technique for a photosensitive lithographic printing plate having a photopolymerizable layer (hereinafter referred to as a photopolymer plate), an inner drum type image recording device is used as a device for recording an image on the photopolymer plate. In the inner drum type image recording device, the photopolymer plate is disposed along the inner peripheral surface of a circular-arc-shaped support. By rotating a spinner mirror which is disposed at the center of the circular arc of the support, a light beam, which is incident on the reflecting mirror surface of the spinner mirror from an axial direction of the spinner mirror, is reflected toward the photopolymer plate and main scanning is carried out. The spinner mirror moves at a uniform velocity in the axial direction, and this movement is subscanning. In this way, light is main scanned and subscanned on the photopolymer plate such that an image is recorded thereon.
In the above-described inner drum type image recording device, the light which is reflected by the spinner mirror and is to be focussed on the photopolymer plate is reflected at the photopolymer plate surface. Depending on the angle of reflection thereof, the light may reach a different position on the photopolymer plate. Because this further reflected light is dispersed light, it is thus not concentrated at one point, and rather, is randomly reflected (reflected scattered light). The effect on the photopolymer plate surface caused by this reflected scattered light is shown in FIG. 9 as a dot percent characteristic based on an image signal expressing uniform halftone dots.
In the case of a negative-type photopolymer plate, a phenomenon known as flare occurs in which the dot percent is high due to the reflected scattered light. As shown in FIG. 9, much flare can be seen at the both ends in the main scanning direction, and flare is great at the subscanning direction rear end side (subscanning completed side) (i.e., there is little flare at the side which has not yet been subscanned).
Other causes of flare in addition to reflected scattered light include the characteristics of the laser beam (the beam diameter, the beam focus, the beam profile, and the like), the extinction ratio of the modulator, the rise time/fall time of the laser, and the like.
Here, in order to mitigate the effect of the reflected scattered light, structures have been proposed in which light-shielding plates called baffles are provided in the radial direction from the rotation axis center of the spinner mirror toward the inner peripheral surface of the support (as one example, see Japanese Patent Application Laid-Open (JP-A) No. 10-162127). A baffle is provided at the front and at the back of the spinner mirror (at both the un-subscanned side and the already subscanned side). A plurality of baffles are provided in order to divide the space above the support into units of predetermined angles. In this way, the light reflected from the spinner mirror does not reach regions at the outer sides of the divided space, and therefore, the reflected scattered light can be reduced by that much.
However, a path for a moving mechanism for placing the photopolymer plate on the peripheral surface of the support must be ensured at the side end portions of the photopolymer plate at the baffles, and there is the possibility that, structurally, a predetermined gap may be formed. As a result, the reflected scattered light leaks from this gap, and flare occurs.
As mentioned above, the conventional baffles are provided at the front and back of the spinner mirror. Therefore, when the spinner mirror must be fixed or serviced, there is little room for the maintenance work to be carried out in, and a secondary problem arises in that workability is poor.
In view of the aforementioned, an object of the present invention is to provide an inner drum type image recording device in which flare can be prevented by suppressing leaking of reflected scattered light from gaps which are required from a structural point of view, while using as few baffles as possible.
A first aspect of the present invention is a device for use in recording an image on a recording medium with a light beam, the device comprising: a support having a surface for supporting a recording medium; a shaft provided substantially parallel to the surface of the support; a mirror provided so as to be rotatable around the shaft and movable along the shaft, and while reflecting a light beam onto the recording medium, the mirror carrying out main scanning by rotating around the shaft and subscanning by moving along the shaft, the mirror having opposite sides along a direction of the subscanning; and a shield provided to be movable with the mirror, on only one side of the mirror, for blocking scattered reflections of the light beam from the mirror.
A second aspect of the present invention is an inner drum type image recording device for use in recording an image on a recording medium with a light beam, the device comprising: a support having an arcuate cross-section, with an inner peripheral surface for receiving a recording medium in contact therewith; a spinner mirror provided so as to be rotatable around an axis extending substantially parallel to the inner peripheral surface of the support, and due to the spinner mirror rotating, a light beam radiating from a direction substantially parallel to said axis is reflected for performing main scanning of a recording medium received on the inner peripheral surface of the support, and while the recording medium is being main scanned, the spinner mirror moves lengthwise along the axis for performing subscanning of the recording medium such that an image is recorded on the recording medium in accordance with the reflected light beam; and a baffle provided along a direction from which the light beam radiates, between the spinner mirror and the light beam for blocking scattered reflections of the light beam from the mirror, the mirror including a rear side facing away from the baffle towards a space substantially devoid of structure for blocking scattered reflections of the light beam reflected by the mirror.
A third aspect of the present invention is a method for blocking scatter reflections of a light beam from a spinner mirror in a drum type image recording device having a drum in which a recording medium is received, the method comprising: (a) main scanning a recording medium in the drum by receiving the light beam with the spinner mirror and rotating the spinner mirror to reflect the light beam circumferentially, relative to the drum, along the recording medium; (b) subscanning the recording medium by moving the spinner mirror lengthwise along the drum, while performing main scanning to reflect the light beam transversely, relative to a direction in which main scanning is performed, along the recording medium; (c) moving a light shield in correspondence with the mirror to impede optical paths in reflection scatter directions from the mirror to sections of the recording medium which have been main scanned with the light beam; and (d) leaving optical paths in reflection scatter directions substantially unimpeded from the mirror to sections of the recording medium, which have not been main scanned.
In accordance with the present invention, a baffle is only placed at the rear side of subscanning movement. Namely, there is no need for a baffle for blocking light at the subscanning front side (the side at which subscanning has not been carried out). The reason for this is that, because the effect of scattered reflected light on the subscanning front side is slight, the image quality does not deteriorate even if no baffle is provided. By keeping the number of baffles to a minimum, space is provided for maintenance work on the spinner mirror or the like, and workability improves.